This invention relates to a digital to analog converting apparatus having an analog to digital converter (hereinafter called "A/D converter") which converts an analog output signal into a digital signal so that the digital signal may be compared with a digital input signal.
There has long been used a digital to analog (D/A) converting apparatus having a plurality of switches, a resistor ladder circuit, an A/D converter, a comparator and a switching control circuit. The switches are opened and closed under the control of the switching control circuit, whereby the resistor ladder circuit divides a power source voltage and generates an analog voltage of a desired value. The analog voltage is applied to the comparator through the A/D converter and is then compared with a digital input signal supplied to the comparator. The output of the comparator is supplied to the switching control circuit. The switching control circuit controls the switches in accordance with the output of the comparator. This sequence of operation is repeated until the two input signals to the comparator have the same value. When the input signals of the comparator are the same, that is, when the output voltage of the resistor ladder circuit is changed to equal that of the digital input signal, the D/A conversion is completed. While the above-described D/A converting apparatus responds very quickly, it requires a large amount of circuitry due to the resistor ladder circuit, and is therefore expensive.